Roof panel assemblies on vehicles are popular for providing and supplementing ventilation in the vehicle and, when a window unit is included, for providing sunlight from the top of the vehicle. It is important that the panel or window unit be capable of being closed in weathertight relationship to the roof and preferably when the panel or window unit is opened, the entire unit is moved away from the weather stripping or sealing structure so as not to cause wear and eventual damage to it. In some structures, the entire window unit is removable for maximum ventilation. See U.S. Pat. No. 3,979,148 to Martin. In such cases, it is desirable that the hinge assembly connecting the window unit to the vehicle roof permit quick and easy detachment and reattachment.